Tires are sometimes desired with treads for promoting traction on wet surfaces. Various rubber compositions may be proposed for such tire treads.
For example, tire tread rubber compositions which contain high molecular weight, high Tg (high glass transition temperature) diene based synthetic elastomer(s) might be desired for such purpose particularly for wet traction (traction of tire treads on wet road surfaces). Such tire tread may be desired where its reinforcing filler is primarily precipitated silica with its reinforcing filler therefore considered as being precipitated silica rich.
In one embodiment, the improved predictive wet traction performance for the tread rubber composition is based on a maximization of its tan delta physical property at 0° C.
However, it is also desired to provide such tread rubber composition containing the high Tg elastomer for wet traction with a lower stiffness at lower temperatures to promote cold weather winter performance, particularly for vehicular snow driving.
In one embodiment, the predictive cold weather performance for the tread rubber composition is based on a minimization of its stiffness physical property at −30° C. (e.g. minimized storage modulus E′).
Therefore, it desirable to provide such vehicular tire tread with a rubber composition containing both high and low Tg elastomers with an optimized (maximized) tan delta property at 0° C. (for predictive wet traction performance improvement) combined with an optimized (minimized) stiffness property at −30° C. (for predictive cold weather performance improvement).
It is considered that significant challenges are presented for providing such tire tread rubber compositions that provide a combination of both wet traction and winter performance. To achieve the challenge of providing such balance of tread rubber performances with tread rubber compositions, it is recognized that concessions and adjustments would be expected.
To meet such challenge, it is desired to evaluate:
(A) utilizing a high vinyl polybutadiene rubber with a high Tg,
(B) utilizing a low vinyl polybutadiene rubber with a low Tg,
(C) providing an inclusion of a traction promoting resin in the tread rubber composition to aid in promoting wet traction for the tread, and
(D) reinforcing filler containing a high content of precipitated silica to also promote wet traction for the tire tread rubber composition.
In the description of this invention, the terms “compounded” rubber compositions and “compounds” are used to refer to rubber compositions which have been compounded, or blended, with appropriate rubber compounding ingredients. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).
The glass transition temperature (Tg) of the elastomers may be determined by DSC (differential scanning calorimetry) measurements at a temperature rising rate of about 10° C. per minute, as would be understood and well known by one having skill in such art. The softening point of a resin may be determined by ASTM E28 which might sometimes be referred to as a ring and ball softening point.